Self-adhering single plies: an emerging technology

Single-ply membranes have become important players in the low-slope roofing market. Products such as EPDM and PVC have been used in the U.S. roofing industry since the late 1970s. TPO has been used as a roof membrane since 1991 and currently is the fastest-growing segment of the low-slope market, according to surveys conducted by NRCA and SPRI. Like all products, single-ply membranes have had their problems. However, they are considered dependable and competitive roof systems.

Many in the roofing industry believe fully adhered single-ply membrane roof systems are the best single-ply roof systems available. There are a number of reasons for this belief, including the following:

• Fully adhered systems have exposed membranes, so it is easier to locate leaks and other membrane problems.
• Unlike mechanically attached systems, which also are exposed membrane systems, there is little stress on the seams from wind and other loads because the seams are supported and reinforced by the substrate. This reduces the risk of seam failure and leaks.
• Fully adhered systems work well on oddly shaped and steep-slope roofs because the adhesives do not slide and the membranes are lightweight, so gravity does not pose a big problem.
• It is easy to design effective vapor-retarder systems, which is not true of, for example, mechanically attached systems.
• Maybe most important, fully adhered systems have the best performance record during the years.

Review of NRCA's 2006-07 Low-slope Roofing Materials Guide, as well as membrane manufacturers' literature and Web sites, has revealed four manufacturers that produce self-adhering, or peel-and-stick, single-ply membrane products—three manufacture TPO membranes and one manufactures PVC membranes. General information about these products is shown in the figure.

Product attributes

Unlike modified bitumen self-adhering products, which have been used since the 1980s, self-adhering single-ply membranes do not have a long history. The first self-adhering single-ply membrane was introduced by GenFlex Roofing Systems LLC, Indianapolis, in 2003. It was based on GenFlex Roofing Systems' TPO membrane and used a factory-applied, high-tack, pressure-sensitive adhesive film. In 2005, Wayne, N.J.-based GAF Materials Corp. began producing a self-adhering TPO membrane. At about the same time, Canton, Mass.-based Sarnafil Inc. (now Sika Sarnafil Inc.) introduced a PVC-based self-adhering membrane system. And just a few months ago, Carlisle SynTec Inc., Carlisle, Pa., introduced a self-adhering TPO membrane. I would expect other manufacturers will enter this market segment if the current products prove successful.

These products have several features in common. Unlike most modified bitumen self-adhering systems, single-ply membrane material cannot serve as an adhesive. So a factory-applied, high-tack, pressure-sensitive adhesive film is applied. These adhesive films are sticky, and little has been revealed about their chemical compositions. They appear to be proprietary because film color differs among manufacturers. To keep the membranes from sticking in the roll or to anything else until they are installed, a layer of release film is installed over the adhesive. The release film must be removed in the field immediately before installation.

As with conventional fully adhered systems, manufacturers provide a list of approved substrates for each self-adhering single-ply membrane, and manufacturers should be consulted before applying one of these membranes to a substrate. In general, all manufacturers allow the use of polyisocyanurate, plywood and oriented strand board. Most also allow wood fiberboard and fiberglass-faced gypsum. The variation in acceptable substrates likely has more to do with which substrates manufacturers have approvals for rather than adhesive performance because older systems appear to have a wider choice of substrates.

Four manufacturers produce self-adhering, or peel-and-stick, single-ply membrane products.

Regarding approvals, all these manufacturers indicate their products meet FM Approvals' 1-90 rating for wind-uplift resistance and some manufacturers indicate their products meet FM Approvals' 1-120 rating for wind-uplift resistance. As always, it is necessary to check with the manufacturer that is supplying the systems for your job to determine the exact wind and fire approvals the systems meet. This is particularly important with self-adhering systems because they are relatively new and manufacturers constantly will be adding to their approvals lists.

White appears to be the most common color among the available products; only one manufacturer lists tan in its literature. This makes sense because white is the most commonly used color for thermoplastic membranes, and, presently, these are not high-volume products. White also will provide the lowest heat load on the adhesive. It is possible some self-adhering adhesives could slide or be damaged at elevated temperatures.

A minimum application temperature of 50 F and rising is listed for all available products. Some manufacturers originally listed 40 F as the minimum application temperature but have increased it to 50 F. Unlike with conventional bonding adhesives, additional drying time will not overcome cold weather's effects. If the adhesive is not tacky or sticky because of cold weather, a primer might help. Some manufacturers allow the application of their products at temperatures as low as 40 F if a special primer is used. If a system has to be installed in cold weather, it is important to ask its manufacturer whether it has a primer system to use in cold weather.

The benefits

One of the biggest benefits of self-adhering single-ply roof systems is reduced labor per square foot. This reduced labor may lead to reduced installed costs. Carlisle SynTec offers data that show the labor required to adhere 5,000 square feet of its self-adhering product is two man-hours with a four-man crew as opposed to 12 1/2 man-hours with a five-man crew to install its conventional fully adhered system. These times exclude sheet layout and seaming, which should be the same for the self-adhering and conventional fully adhered systems.

Most labor savings come from not having to apply contact adhesive and wait for it to dry before installing sheets. Based on discussions I have had with contractors who have installed self-adhering single-ply roof systems, I have found contractors generally believe them to be about equal in cost with conventional fully adhered systems. Because self-adhering single-ply roof systems are fairly new to the industry, none of the contractors I spoke with had used the material on more than one or two jobs, so their crews are still learning how to install them.

Another benefit users can experience is reduced likelihood of improper application of bonding adhesive. The two most common adhesive application mistakes I hear about are applying too little adhesive and applying adhesive to only one surface instead of both. By applying adhesive in the factory, the correct amount is applied. And because a pressure-sensitive adhesive is used with self-adhering systems, it only needs to be applied to one surface. Another related benefit is dirt cannot be blown into the adhesive while it is drying as can happen with conventional bonding adhesives.

There also are fire and worker safety issues that self-adhering roof systems avoid. The solvent systems in many contact adhesives are volatile and flammable with flash points below 0 F. Any spark can cause a flash fire. In addition, the solvents are not healthy for workers to be near. Overexposure can result in headache, dizziness, fatigue or nausea. Skin and eye irritation from prolonged and/or repeated contact also are possible side effects.

Self-adhering systems also offer benefits related to not having to use bonding adhesives. The relative value of these benefits will depend on particular job requirements. Because bonding adhesives—including most water-based bonding adhesives—contain solvents, they release volatile organic compounds (VOCs), which are related to smog generation. Therefore, in parts of the U.S., such as southern California, there are limitations on their use. Factory-applied adhesives are 100 percent solid, so they do not release any VOCs.

The disadvantages

Self-adhering roof systems do have some shortcomings. The biggest disadvantage in my opinion is high material cost. Self-adhering sheets cost about 40 cents more per square foot than conventional membranes and contact adhesives. The cost per square foot will vary depending on job size and U.S. region.

A second issue is self-adhering systems are more susceptible to acquiring dirt and dust on their surfaces. Unlike conventional fully adhered systems, the liquid adhesive will not encapsulate dirt and dust during the application process. Although encapsulated dirt obviously does not improve adhesive performance of conventional fully adhered roof systems, the adhesive will stick well enough to work. The same cannot be said for self-adhering systems where dirt could coat the adhesive layer and act like a release agent.

Another potential problem is the adhesive film's aggressiveness. If workers are not careful after removing the release film, the sheet will stick to anything it contacts, including the back of the release film, the finished membrane, etc. When it sticks, it is difficult to remove, and even if it can be removed, that section of the sheet cannot be reused. As a result, there is potential for increased waste.

Seaming methods

There are two methods used to seam self-adhering systems. One seaming method common to all manufacturers is conventional heat-welded seams. Another method, offered by two manufacturers, is a self-adhering seam. The claimed benefit of a self-adhering seam is the speed by which the seam can be completed. A downside is that because the adhesives used are 100 percent solid, there is nothing that can flow to fill in minor imperfections, such as the molten plastic in conventional heat-welded seams.

There have been accounts of leaking, or "weeping," seams with single-ply and modified bitumen self-adhering products. A theory is that minor imperfections in the seam area keep 100 percent contact from occurring, and then water can penetrate these small channels into the seams. In an attempt to prevent this potential problem, self-adhering seams are several times wider than conventional 1 1/2-inch heat-welded seams. Time will tell whether this solution works.

To keep factory-applied adhesive off end laps to allow heat-welded or self-adhering seaming, all the manufacturers butt end laps and overlay the end-lap seams with a membrane strip that is heat-welded or self-adhered. This approach also reduces the chances of leaks caused by "T" seams.

A promising future

Self-adhering technology is showing a lot of promise, but like all new technologies, time will be the final judge of its success. If it succeeds, it would offer a way to reduce the cost of fully adhered single-ply systems. It also would overcome many issues associated with solvents in bonding adhesives and could cause fully adhered systems as we know them to be used less frequently.

Ted Michelsen is president of Michelsen Technologies LLC, Lakewood, Colo., a roof consulting firm.